The above-mentioned handwheels for such tilting bearings are, in general, circular disk-shaped castings, which have reduced material thickness in the center of the disk compared with the circumference of the disk. The circumference of the disk is therefore thickened in the manner of a torus and leads to an essentially toroidal circumferential surface, which extends between the two front-side surfaces of the disk over an angle of circumference of about 270.degree. in relation to the center of the circular surface, which forms the radial cross section of this toric disk circumference. The value of this angle of circumference of greater than 180.degree. is predetermined by the reduced thickness of material in the center of the disk. Depending on the deviating size of the material thickness in the center of the disk, the angle of circumference may consequently also be greater or smaller than 270.degree., as a consequence of which the toroidal circumferential surface of the handwheel will also be correspondingly larger or smaller for the machining.
Machining of the toroidal circumferential surface of such handwheels has hitherto been performed on a turning machine, in which the cutting tool, which is maintained in contact with the surface being machined on the casting being rotated by the work spindle of the turning machine, is clamped onto the slide of the cutting machine. However, this arrangement of the turning tool does not make it possible to machine the torus surface in one pass over the entire angle of circumference, but the casting must be turned by 180.degree. after a first partial machining of only one part of the toroidal circumferential surface and be remounted on the work spindle of the turning machine, so that the remaining part of the toroidal circumferential surface can then be machined from the opposite front surface of the casting. Not only is this machining correspondingly time-consuming and expensive, but it is also impossible to achieve a better surface finish by this machining, so that the machining with the turning tool usually must be followed by a finishing for preparing the desired polished surface.